The speed of wafer process is often gated by the “vent up” and “vent down” time spent in the loadlock of a processing tool. This speed was greatly increased in the 1990's with the introduction of load lock diffusers (porous membranes) which allowed fast venting of chambers without creating turbulent gas patterns which might disturb particles thus contaminating the work. Examples of these diffusers include the Entegris ChamberGard™ (available from Entegris, Chaska, Minn.) line of products based on Nickel membrane. Due to the nature of this membrane, the diffusers also act as particle filters, offering 3 nanometer filtration with up to 9 Log Reduction Value (LRV) (i.e., removal of 99.9999999% of contaminants).
ChamberGard™ flat sheet diffuser (membrane), known as FV-50, is designed for a maximum operating pressure of 45 psid. At this pressure, it has a warranted lifetime of 100,000 cycles. Higher numbers of cycles would be beneficial for today's single wafer tools. The FV-50 is a product made by the sintering of a 2-micron nickel powder into sheets that are 0.100 inches thick and 65% porous. The material provides an LRV value of 9 down to the particle size of 3 nanometers. The material is ideally suited as a diffuser (membrane) with the fine pore structure diffusing the gas uniformly over the surface.
In recent years, and particularly with single wafer processing, there is a need to further increase the vent speed of loadlock chambers. Many end users have increased the inert gas supply pressure to the chamber diffusers to increase the flow rate and reduce the vent time. As a consequence, the number of lifecycles has also increased dramatically. The loadlock diffuser/filters are being subjected to higher pressures and more cycles then they were designed to handle.
Current metal diffusers (membranes) also act as high efficiency filters. These filters are high surface area and high porosity bodies made by the sintering of fine metal particles (not more than 10 micron in average size). These materials, while strong and robust when compared to polymeric materials, have their limitations. This is particularly the case when dealing with flat sheets. Because single wafer chambers are by design very shallow to minimize volume, the use of a flat sheet diffuser (membrane) has been shown to be vastly superior than tubular elements, providing a much smoother gas flow while taking up less chamber volume.
There exists a need for a filter/diffuser that can be produced in a form of a flat sheet, can withstand high gas pressures over several million cycles without creating gas turbulence in the chamber, all while offering high efficiency particulate filtration.